Alloantigens & Superantigens

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Alloantigens & Superantigens

Alloantigens

  • These are the antigenic substances, carried by various individuals of a given species.
  • For instance, a great set of alloantigens was identified in red blood cells of mammalian species.
  • Alloantigens stimulate the immune system of the host against foreign antigens causing alloimmunization and subsequent production of alloantibodies which caused decreased survival of blood cells in vivo
  • At first, it was found that human erythrocytes contain at least two main blood antigens (agglutinogens A and B), whereas the sera of individuals carry beta- and alpha-agglutinins (antibodies).
  • On the basis of AB0 antigenic structure, the erythrocytes of all people can be subdivided into 4 main groups.
  • More than 15 systems of blood alloantigens (e.g., M and N systems, Kelly, Duffy, etc.) including about 100 antigens are known to date.
  • Besides AB0 system, 85% of humans possess erythrocytes expressing rhesus factor (Rh) antigen (so-called rhesus-positive persons), while other 15% of individuals are rhesus-negative.

Alloantigens & Superantigens

Superantigens

  • There is a particular group of antigens, known as superantigens. They display outstanding biological features being active in the lowest concentrations.
  • They interact with the MHC class II molecules and T cell receptors.
  • A small dose of these lead to the activation of a great set of T cells in more than 20% of their total quantity (in comparison, conventional antigens activate not more than 0.01%-0.1% of all T lymphocytes).
  • Similar to ordinary antigens, they are recognized by T cells via TCR. However, superantigens have the strong binding capacity to some common variable domains of T cell receptors (their Vb-variants).
  • Consequently, they activate a great number of T-lymphocytes that is followed by redundant pro-inflammatory cytokine production by T cells and macrophages (IL-1, IL-2 IL-6, IL-12, TNF-alpha, etc.) Such activation provokes inflammation with severe tissue damage.
  • A large number of bacterial toxins (staphylococcal, streptococcal toxins, enterotoxins, etc.) pertain to superantigens.

Alloantigens & Superantigens

differences between the ways in which a conventional antigen and a superantigen bind to MHC class molecules and the TcR.

References

  1. https://www.sciencedirect.com/science/article/pii/S0969212697002529
  2. https://www.researchgate.net/figure/Schematic-illustration-of-three-alloantigen-recognition-pathways-A-Direct_fig1_337340672